1. Field of the Invention
This invention relates to conductive polymer compositions.
2. Introduction to the Invention
Conductive polymer compositions exhibiting PTC behavior, and electrical devices comprising them, are well known. Reference may be made, for example, to U.S. Pat. Nos. 2,952,761; 2,978,665; 3,243,753; 3,351,882; 3,571,777; 3,757,086; 3,793,716; 3,823,217; 3,858,144; 3,861,029; 3,950,604; 4,017,715; 4,072,848; 4,085,286; 4,117,312; 4,177,376; 4,177,446; 4,188,276; 4,237,441; 4,242,573; 4,246,468; 4,250,400; 4,252,692, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,314,231, 4,315,237, 4,317,027, 4,318,881, 4,327,351, 4,330,704, 4,334,351, 4,352,083, 4,388,607, 4,398,084, 4,413,301, 4,425,397, 4,426,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216, and 4,442,139; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; and commonly assigned U.S. Ser. Nos. 601,424 now abandoned, published as German OLS No. 1,634,999; 732,792 (Van Konynenburg et al), now abandoned, published as German OLS No. 2,746,602; 798,154 (Horsma et al), now abandoned, published as German OLS No. 2,821,799; 134,354 (Lutz); 141,984 (Gotcher et al), published as European Application No. 38,718; 141,988 (Fouts et al), published as European Application No. 38,718, 141,989 (Evans), published as European Application No. 38,713, 141,991 (Fouts et al), published as European Application No. 38,714, 150,909 (Sopory), published as UK Application No. 2,076,106A, 184,647 (Lutz), 250,491 (Jacobs et al) and 254,352 (Taylor), published as European Application No. 63,440, 272,854 and 403,203 (Stewart et al), published as European Patent Application No. 67,679, 274,010 (Walty et al), 300,709 and 423,589 (Van Konynenburg et al), published as European Application No. 74,281, 349,505 (McTavish et al), published as European Application No. 87,884, 369,309 (Midgley et al), 380,400 (Kamath), published as European Application No. 96,492, 474,390 (Leary), 483,633 (Wasley), 485,572 (Nayak et al), 493,445 (Chazan et al), 493,390 (Leary et al), 509,897 (Masia et al), 524,482 (Tomlinson et al), 534,913 (McKinley), 535,449 (Cheng et al) 552,649 (Jensen et al), 573,099 (Batliwalla et al), 904,736, published as UK Pat Nos. 1,470,502 and 1,470,503, 628,945 (Carlomagno), and 650,918, 650,920 and 650,919 (Batliwalla et al) (MP0959, 961 and 962). The disclosure of each of the patents, publications and applications referred to above is incorporated herein by reference.
Particularly useful devices comprising PTC conductive polymers are circuit protection devices. Such devices have a relatively low resistance under the normal operating conditions of the circuit, but are "tripped", i.e., converted into a high resistance state, when a fault condition, e.g., excessive current or temperature, occurs. When the device is tripped by excessive current, the current passing through the PTC element causes it to self-heat to an elevated temperature at which it is in a high resistance state. The increase in resistance is accompanied by an expansion of the PTC element along an expansion axis. Such devices, and PTC conductive polymer compositions for use in them, are described for example in U.S. Pat. Nos. 4,237,411, 4,238,812; 4,255,698; 4,315,237; 4,317,027; 4,329,726; 4,352,083; 4,413,301; 4,450,496; 4,475,138; and 4,481,498 and in copending commonly assigned U.S. Application Ser. Nos. 141,989, 524,482 now U.S. Pat. No. 4,562,313 and 628,945, and in commonly assigned patent applications by Ratell, Ser. Nos. 711,907 and 711,908, by Au et al, Ser. No. 711,910, and Carlomagno, Ser. No. 711,790. The disclosure of each of these patents and pending applications is incorporated herein by reference. Ser. No. 141,989, which has been published as European Application No. 38,713, discloses that the addition of an arc-controlling additive such as alumina trihydrate to a conductive polymer results in improved performance under electrical stress and that compositions containing such additives are, therefore, particularly useful for circuit protection devices.